1. Field of the Invention
The present invention relates generally to electrical devices or systems. Specifically, the present invention relates to a self-test system for an electrical device or system with at least one microcontroller or microprocessor.
2. Brief Description of the Related Art
In factory testing of an electrical device or system with a microcontroller or a microprocessor, it is important to discover any flaws in the device's components.
Conventionally, a `bed of nails` test is used to test a microcontroller-controlled device and its components. The bed of nails test typically involves placing a number of test pads on all electrical nodes of a device's circuit board, providing an electrical stimulus and observing the response. The bed of nails test examines the interconnections between different portions of the device's circuitry and the function of individual integrated circuits (ICs).
Designing a bed of nails test method for a particular type of device and acquiring the proper equipment (e.g. test fixtures) required for a bed of nails test are relatively expensive. Another disadvantage is the amount of time required to run the bed of nails test for each device on an assembly line. For example, a typical bed of nails test for a portable communication handset may take four to six minutes per handset. Two important goals in manufacturing are to minimize costs and minimize the time for testing each device. The longer the testing process, the more inefficient and expensive it is.
Furthermore, for devices with high-density circuits, there may be insufficient space on the device's circuit board to put the test pads on all the nodes or at least a sufficient number of nodes to detect and locate all faults. For integrated circuits, testing nodes are even more difficult. In some cases, the design of the device is modified, such as supplying test points or extra interconnectors, to enable a bed of nails test. These modifications to the device further increase the cost of and the amount of time associated with a bed of nails test.
Boundary scan testing is another method used by some manufacturers. But boundary scan testing requires a certain number of pins on the integrated circuits to be dedicated to this testing task. Moreover, boundary scan testing is not very effective on circuits with many discrete components.